1. Field of the Invention
The present invention relates to an apparatus such as an electric furnace, a gas furnace, a steam furnace, etc., and more particularly to a temperature control simulation method and apparatus for developing a temperature control algorithm and learning a temperature control manipulation process in such a process apparatus without using an actual furnace.
2. Description of the Related Art
A temperature control simulation in a semiconductor manufacturing apparatus using an electric furnace is known.
FIG. 32 is a block diagram which shows an electric furnace of a vertical diffusion apparatus used as a semiconductor manufacturing apparatus. The electric furnace system, as illustrated in FIG. 32, includes a heater 1101 for heating a furnace, a heater thermo-couple 1102 for detecting the temperature of the heater 1101, a cascade thermo-couple 1105 for detecting the temperatures of intermediate portions between a uniform heating tube 1103 and a reaction tube 1104, a boat 1106 mounted thereon with a wafer to be heat-treated, and a temperature controller 1107 for calculating a quantity of manipulation (i.e., a value of electric power) Z applied to the heater 1101 based on the detected temperatures of the heater thermo-couple 1102 and the cascade thermo-couple 1105 and a preset temperature Y.
Heater 1101 is divided into a plurality of zones to control the furnace temperature with higher accuracy, and for instance, in the case of a four-zone division, the divided zones are sequentially called a U, CU, CL and L zone, etc., in order from top to bottom.
The heater thermo-couple 1102 and the cascade thermo-couple 1105 are disposed in each divided zone, and the quantity of manipulation Z given to the heater 1101 is calculated by an algorithm (e.g., PID arithmetic operations, etc.) in the temperature controller 1107 to adjust the value of electric power supplied to the heater 1101 while detecting the temperature of the heater thermo-couple 1102. This adjusts the detected temperature of the cascade thermo-couple 1105 to the set temperature Y.
Also, the boat 1106 having a wafer to be heat-treated, is inserted into the furnace, and is withdrawn after the wafer has been heat-treated. Subsequently, a new wafer to be heat treated is mounted on the boat 1106, which is again inserted into the furnace for heat treatment.
In the case of the vertical diffusion apparatus having an electric furnace as shown in FIG. 32, a process shown in FIGS. 33(a) and 33(b) is performed.
FIG. 33(a) shows a flow chart for one example of a treatment process performed by the vertical diffusion apparatus, and FIG. 33(b) schematically shows a temperature change in the furnace during the process treatment.
Step S1 is a process in which the furnace temperature is settled or stabilized at a comparatively low temperature T0. In step S1, the boat 1106 has not yet been inserted into the furnace.
Step S2 is a process (boat loading) in which the boat 1106 is inserted or loaded into the furnace.
As the temperature of the wafer is usually lower than the target temperature T0, the temperature in the furnace temporarily falls below the target temperature T0 as a result of the boat loading.
A quantity of manipulation to the heater is adjusted by the temperature controller 1107 to allow the furnace temperature to quickly recover from this temperature fall, and to stabilize it at the target temperature T0 within a slight temperature-variation range.
Step S3 is a process (e.g., ramp up) in which the temperature in the furnace is gradually raised or ramped up from the first target temperature T0 to a second target temperature T1 where the wafer is subjected to a process treatment such as layer-forming or deposition processing, etc.
When ramped up, the temperature in the furnace will rise in a delayed manner with respect to a target temperature, so a time period is required until the furnace temperature has been stabilized at the target temperature T1 within a slight temperature range.
Step S4 is a process in which the temperature in the furnace is stabilized at the target temperature T1 so as to subject the wafer to a treatment process.
Step S5 is a process in which the temperature in the furnace is gradually lowered from the second target temperature T1 to the comparatively low first target temperature T0.
Step S6 is a process in which the boat with the mounted wafer which has been subjected to the treatment process and is pulled out of the furnace.
Since steps S1 to S6 are repeated, performing each step in a shortened time leads to an improvement in productivity. In particular, regarding temperature control performance, it is necessary to shorten the time (settling time) required to settle or stabilize the furnace temperature at the target temperature, within a slight temperature range after loading of the boat with the wafer and ramping up the furnace temperature.
Therefore, for shortening the settling time during the boat loading and the furnace temperature ramp-up operation, as well as for conducting maintenance, design engineers for the semiconductor manufacturing apparatus and workers at the semiconductor manufacturing sites frequently must operate or manipulate the temperature controller while monitoring the temperature in the furnace.
The development of the temperature control algorithm and learning the temperature control operation have been accomplished by performing the process treatment as shown in FIG. 33(a) so as to control the temperature while using the apparatus shown in FIG. 32.
However, the apparatus of FIG. 32 is very expensive, requires a large installation space, and is dangerous because of the very high target temperatures at T0 and T1 ranging from about 300 degrees C. to about 500 degrees C. for T0 and from about 800 degrees C. to 1200 degrees C. for T1. In addition, some apparatuses use poisonous gases, so it is essential to carefully manage temperature control. Moreover, it requires more than about 3 to 6 hours to perform steps S1 through S6. Therefore, a method of reducing the costs and shortening the operating time is required.
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional process apparatus, the present invention has been devised, and it is an object of the invention to provide a temperature control simulation method and apparatus which can form, on a computer, a temperature simulation model for a process apparatus, such as an electric furnace, a gas furnace, a steam furnace, etc., which shows substantially the same temperature change as in an actual furnace. Thus, one may develop a temperature control algorithm and/or learn a temperature control manipulation method without using the actual furnace.
To achieve the above object, according to one aspect of the present invention, there is provided a temperature control simulation method in which transfer function means, representative of a relationship between an input to a heater and a temperature output thereof, is determined so that temperature control on a heating furnace can be performed by using the thus determined transfer function mechanism as that of a temperature system simulation device.
In a preferred form of the temperature control simulation method of the invention, the transfer function means comprises a heater system transfer function and a furnace system transfer function. By approximating each of these transfer functions as Kxc2x7exp(xe2x88x92Ls)/(1+Ts), a total transfer function for the entire system is given by the following formula:
K1xc2x7exp(xe2x88x92L1s)/(1+T1s)xc3x97K2xc2x7exp(xe2x88x92L2s)/(1+T 2s)xe2x80x83xe2x80x83(1)
where K is a gain, T is a time constant, L is a delay, suffix 1 indicates the heater system, and suffix 2 indicates a parameter of the furnace system.
Thus, the temperature control simulation for the heating furnace is obtained by using the total transfer function for the entire system.
In another preferred form of the temperature control simulation method of the invention, the transfer function has a parameter which changes over time in accordance with a temperature control process.
In a further preferred form of the temperature control simulation method of the invention, the time constants T1 and T2 of formula (1) change over time.
In a still further preferred form of the temperature control simulation method of the invention, the temperature control process includes controlling a temperature of the heating furnace during a time when a boat is loaded into the heating furnace, and the parameter of the transfer function means, which changes over time, comprises a time constant.
In a yet further preferred form of the temperature control simulation method of the invention, the time constant of the transfer function means is made to change over time during the boat loading, to represent an increase in the heat capacity with a model.
In another preferred form of the temperature control simulation method of the invention, the change over time is given by a second order delay curve.
In a further preferred form of the temperature control simulation method of the invention, the change over time of each of the time constants upon boat loading is expressed by using the following second order delay curve function and time constants Ta and Tb before and after the boat loading.
1+(xcex1xc2x7exp(xe2x88x92t/xcex1)xe2x88x92xcex2xc2x7exp(xe2x88x92t/xcex2))/(xcex2xe2x88x92xcex1)xe2x80x83xe2x80x83(2)
where xcex2 and xcex1 are constants experimentally determined, and t is a period of time.
In a further preferred form of the temperature control simulation method of the invention, the heating furnace includes a plurality of heating zones, and the heater comprises a plurality of heaters, one for each of the plurality of heating zones, and the transfer function means includes interference between the heating zones. If the heaters are provided in the plurality of heating zones, a heater in one heating zone influences the other zones.
For this reason, the transfer function means includes interference between the heating zones, thus making it possible to execute simulation by the transfer function means with high accuracy.
In a further preferred form of the temperature control simulation method of the invention, the transfer function means is determined by measuring an output of the furnace when a stepped input is applied to one of the plurality of heaters, repeating the process of measuring an output of the furnace for all the remaining heaters, and calculating the transfer function means based on the outputs of the furnace.
In a further preferred form of the temperature control simulation method of the invention, the transfer function means is determined from a stepped response of each of the heaters by calculating a temperature output response value of each of the heaters when a stepped input is applied to an associated heater, calculating a temperature output of each of the heaters when a constant input is applied to an associated heater at the same point of time as when the stepped input is applied to calculate a change over time of the temperature output of each of the heaters, and calculating the transfer function means based on the temperature output response value which is subtracted by the change over time of the temperature output of each of the heaters to cancel variations in a power supply which supplies electric power to the heaters.
With this arrangement, when parameters of the transfer function means are determined from the stepped input and the output, errors due to variations in the power supply voltage can be canceled.
In a further preferred form of the temperature control simulation method of the invention, the transfer function means comprises a plurality of transfer functions corresponding to a plurality of different temperature zones, and the plurality of transfer functions are switched among themselves to select the appropriate one corresponding to each one of the plurality of temperature zones.
When each transfer function is approximated by the above formula (1), the parameters of the transfer functions can change according to the respective temperature zones of the system.
Therefore, to effect such an approximation as accurately as possible, it is preferable that the entire temperature range used for the temperature control be divided into a plurality of temperature zones, and the parameters of the transfer functions be determined according to the respective temperature zones.
According to another aspect of the present invention, there is provided a temperature control simulation apparatus with a temperature system simulation device adapted for use in a temperature control simulation as discussed above; and a temperature controller for determining an input to the temperature system simulation device based on an output thereof With this arrangement, it is possible to simulate the temperature control in the same manner as an actual heating furnace is controlled, thus enhancing the training experience.
In a preferred form of the temperature control simulation apparatus of the invention, the apparatus has a converter for converting temperature information which is generated by the temperature system simulation device into a corresponding voltage signal.
In a further aspect of the present invention, there is provided a semiconductor manufacturing apparatus having the above temperature control simulation apparatus.
According to a further aspect of the present invention, there is provided a method of acquiring a transfer function, including defining an object to be controlled in a temperature system, which includes a heater for heating a furnace, by a series-type transfer function which includes a heater system transfer function and a furnace system transfer function, determining the heater system transfer function based on a relationship between an input to the heater and an output of a heater thermo-couple, and determining the furnace system transfer function based on a relationship between an input to the heater and an output of a cascade thermo-couple and based on the heater system transfer function determined above.
In a preferred form of the transfer function acquisition method of the invention, using the above-mentioned formula (1), the heater system transfer function is first determined based on an output of a heater thermo-couple, which is constructed, for example, as shown in FIG. 1, in response to a stepped input, and the furnace system transfer function is then determined based on an output of the cascade thermo-couple, and the heater system transfer function already determined.
In a preferred embodiment of the temperature control simulation apparatus of the invention, as illustrated in FIG. 1, the heating furnace includes M (e.g., 4) heating zones with a plurality of heaters, and a temperature rising pattern is formed in each heating zone when the power supply to an arbitrary one of the heaters is increased in a stepwise manner. The respective temperature rising patterns in the respective heating zones are detected by N (e.g., 4xc3x972) thermometers (e.g., 4 heater thermo-couples and 4 cascade thermo-couples) disposed in the respective heating zones, and the detection results are stored in a memory over all the heaters.
Subsequently, from the Mxc3x97N patterns thus detected and stored, Mxc3x97N transfer functions are approximately determined for obtaining a temperature output of an arbitrary heating zone against an input to an arbitrary heater. Thus, the respective transfer functions are input in a computer as a temperature system simulation model of a heating furnace.
In another preferred embodiment of the temperature control simulation apparatus of the invention, a temperature change in the heating furnace upon loading an object to be heat-treated is represented by changing the heat capacity of a simulation model over time, so that temperature control on the heating furnace under external disturbances can be simulated on the computer.
In a further preferred embodiment of the temperature control simulation apparatus or system of the invention, the temperature system simulation device input in a computer and the temperature controller provided for controlling the temperature of the heating furnace are mutually connected together. The temperature system simulation device input to the computer can be made a control target in the form of a virtual furnace in place of the actual object (e.g., the actual furnace) to be controlled by the temperature controller.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-228770, filed Aug. 13, 1998, which is expressly incorporated herein by reference in its entirety.